This chapter dives deep into one of the maintenance headaches of managing telemetry systems: cardinality in your storage systems. Here is the definition of cardinality from chapter 1:
Definition
Cardinality is the term for index complexity—specifically, the number of unique combinations the fields in the index may produce. If you have fields A and B, where A has two possible values and B has three possible values, the cardinality of that index is A * B, or 2 * 3 = 6. Cardinality significantly affects search performance no matter what data storage system is being used.